(191aa) Oxidation-Reduction Potential Controlled Microaeration for Fermentation of Lignocellulose Feedstock

The dilute acid pre-treatment of pine lignocellulose produces inhibitors (acetic acid, furfural, and 5-hydroxymethylfurfural) that decrease specific cell growth rate and ethanol productivity during fermentation. Concentration of this fermentation feedstock via nanofiltration results in increased initial glucose concentrations and higher final ethanol titers, both of which further inhibit fermentation. Previous work with very high gravity fermentation has shown that oxidation-reduction potential (ORP) controlled microaeration (MA) increases cell growth rate and ethanol productivity when the fermentation is inhibited by glucose and ethanol. The goal of this study was to apply this same ORP-controlled microaeration strategy to a mock lignocellulose hydrolysate feedstock (LHF) to determine the effect of microaeration on fermentation kinetics, and to determine if microaeration can reduce fermentation costs compared to traditional unaerated (UA) (strict anaerobic) fermentation. It was found that microaeration (ORP controlled at -150 mV) during LHF fermentation increased the specific ethanol productivity by 250% (Q_UA,P=0.51 vs. Q_MA,P=1.32) during exponential growth with no reduction in ethanol yield (Y_P/S=0.49). Additionally, higher specific inhibitor reduction rates (furfural; 0.13 vs. 0.25 g/L/OD/hr, and HMF; 0.02 vs. 0.06 g/L/OD/hr, for UA vs MA, respectively) were observed. When the experimental results were applied to an economic assessment for a 5 MGPY LHF to ethanol plant, it was found that microaeration resulted in an increase in fermentation EAOC of $2.19 million/yr. The results indicate that microaeration is not a more economical mode of operation for LHF fermentation than traditional unaerated fermentation.